Enhanced Light Absorption and Photo‐Generated Charge Separation Efficiency for Boosting Photocatalytic H2 Evolution through TiO2 Quantum Dots with N‐Doping and Concomitant Oxygen Vacancy

Abstract Low‐range light absorption and rapid recombination of photo‐generated charge carriers have prevented the occurrence of effective and applicable photocatalysis for decades. Quantum dots (QDs) offer a solution due to their size‐controlled photon properties and charge separation capabilities. Herein, well‐dispersed interstitial nitrogen‐doped TiO 2 QDs with stable oxygen vacancies (N‐TiO 2−x ‐V O ) are fabricated by using a low‐temperature, annealing‐assisted hydrothermal method. Remarkably, electrostatic repulsion prevented aggregation arising from negative charges accumulated in situ on the surface of N‐TiO 2−x ‐V O , enabling complete solar spectrum utilization (200–800 nm) with a 2.5 eV bandgap. Enhanced UV‐vis photocatalytic H 2 evolution rate (HER) reached 2757 µmol g −1 h −1 , 41.6 times higher than commercial TiO 2 (66 µmol g −1 h −1 ). Strikingly, under visible light, HER rate was 189 µmol g −1 h −1 . Experimental and simulated studies of mechanisms reveal that V O can serve as an electron reservoir of photo‐generated charge carriers on N‐doped active sites, and consequently, enhance the separation rate of exciton pairs. Moreover, the negative free energy (−0.35 V) indicates more favorable thermodynamics for HER as compared with bulk TiO 2 (0.66 V). This research work paves a new way of developing efficient photocatalytic strategies of HER that are applicable in the sustainable carbon‐zero energy supply.